1. Field of the Invention
This invention relates to a storage stable, polymer-modified asphalt paving binder and a pavement mixture containing the binder.
2. Discussion of Related Art
Asphalt binders for open graded hot mix pavement typically contain from about 15 to about 20 wt. % reclaimed tire rubber to ensure proper viscosity for flow resistance and ease of handling during construction. However, such binders have the disadvantage of emitting fumes from the hydrocarbon process oil used in making the tires. As such, it would be desirable to have available an asphalt paving binder that had the proper viscosity and ease of handling features associated with rubber modified paving binders but did not contain the hydrocarbon process oil.
Frequently, polymeric materials have been added to asphalt products to enhance their rheological properties, i.e., to improve its creep resistance above about 20.degree. C. (See, for example, U.S. Pat. No. 4,371,641, which discloses that roofing bitumen containing a neutralized sulfonated terpolymer such as a terpolymer of ethylene, propylene, and a diene monomer (EPDM) has excellent oxidation stability, U.V. stability, and good creep resistance.) Polymer modified asphalts must also have good phase compatibility between the asphalt and polymer, and be storage stable at high temperatures for ease of handling and application. Compatibility between the polymer and asphalt is very important to ensure that the properties of both are transferred to the finished product for good long term performance. Poor storage stability will render the polymer modified asphalt less desirable for use in paving binder applications, roofing applications, and other industrial specialty products. (See, for example, U.S. Pat. No. 4,873,275, which discloses that paving binders can be made storage stable and more creep resistant by the addition of a copolymer of ethylene with vinyl acetate, alkyl acrylate, or alkyl methacrylate).
However, neither patent nor the references cited therein (all of which are incorporated herein by reference) discloses the particular asphalt paving binder described below.